Green Fluorescent Protein or GFP

When someone first shows up in our lab, the prime goal I set up for him or her is to make “green cells” – I mean to introduce a Green Fluorescent Protein into a mammalian cell culture. In order to be able to perform this one has to know some basic molecular biology. One has to know what a cell is, what the difference is between a prokaryote and an eukaryote cell; what the central dogma is namelly that the information flows from DNA to RNA and from here to proteins is, or as it has been formulated originally and still correctly, the information flows from nucleic acids towards proteins (albeit I assume we will see exceptions for this rule, too). (You can reach a very good lecture on this topic here.) One has to know what the difference between DNA and RNA is, in most basic approach the chemical difference is minuscule (there is a deoxyribose in the backbone of the DNA and a ribose in the RNA, there are other differences but this is the most prominent), while the results are spectacular. DNA is a quite stable molecule that can be degraded by DNAses. DNases require divalent metal ions for their activity ( usually Mg, but other divalent ions can be used too), and we can remove these ions from solutions with so called chelating agents. Most commonly we use EDTA for this task.

From practical point of view, one needs to have some backgrounds in order not to be lost in a molecular biology lab as it follows:

One has to be able to use pipettes (as seen in the previous posts), to make buffers, to know about pH, know what molarity is, and have a good basic background in maths (just enough to calculate the compositions of the buffers).

But you can perform the most basic experiment of DNA isolation even in the kitchen! At the end of this experiment you will be able to even SEE the DNA!

You can extract DNA from any cell, but the easiest way is to use some germs, like wheat or bean germs, soya germs and so on… In the following video you can see the procedure. If you do not have isopropyl alcohol (I don’t have at home for example) use regular ethanol or a strong spirit with at least 70% alcohol content!

Regarding RNA, the world of RNA is a transient world. RNA is degraded by enzymes that can be found everywhere. RNAses can not be blocked by removing metal ions with EDTA. This makes the half life of RNA very short. Let us take the analology of the computer: DNA is like the information on the hard disk, one might have a software on the computer without using it- this is the information in the DNA. If one double clicks on its icon, the program starts, this corresponds to the transcription: information is transcribed from DNA to RNA, or the software is running, even if it is not yet in use, it is ready to get an input and process it into the output. The RNA is similarly translated by ribosome into proteins: these are the products that have been coded in the DNA. Or according to the computer analogy you create a document with the word processor software. The document is an entity by itself. You can print it and have it. If you turn off your computer, the temporary files are destroyed, all unsaved files are deleted. So is with the RNA. RNA is carrying an information for a short period of time, it has a short half life, but can be regenerated from the DNA. These processes are explained in the following video:

Ok, so how do we make green cells? Green flourescent protein is encoded in the genome of the Jelly fish. The protein once identified can be introduced into other organisms if we isolate the DNA sequence that is encoding the GFP protein. So let’s have a look to these wonderful organisms!

Beautiful Jelly fish

The discovery of GFP protein and their mode of action changed plenty of studies in biology. The Nobel Prize for Chemistry in 2008 was given for the identification of the GFP protein and its way of action. You can see below two videos about the topic. A detailed, in depth one or below a short overview of the topic. You choose!

Giving green light to biology

Nobel Prize for GFP

After this overview I think it is time to have an experiment. We will see how you can introduce the GFP encoding DNA into a bacteria. For this we use so called plasmids as a vector. We call vector in biology a tool that is able to carry genetic information, like a plasmid, cosmid, or a virus. A plasmid is a small circular DNA that is able to self-replicate into a bacteria and to express a protein. They are responsible for lateral gene transfer in bacteria, e.g. transfering antibiotic resistance gene from one bacteria to a different one.

In the following experiment we will see the introduction of a GFP encoding DNA into a so called Agrobacterium, a bacteria that is infecting plants.

Introducing the GFP into a bacteria

Cool, isn’t it?

We can make even more complicated investigations with the help of the GFP. In the following animation it is shown the transfection process in a mammalian cell where the addressed question is if two proteins interact or not? For this they use the so called FRET or fluorescence resonance energy transfer. In order to see if the two proteins are close to each other or not, we have to use two GFP like tagged proteins with their excitation and emission wave lengths close to each other. See how it works:

Investigating protein-protein interactions with fluorescent proteins

GFP has several other applications, like tracing of migrating neurons, as seen in the following video:

Or full GFP organisms like in the following one:

If you would like to know even more about the GFP protein, please visit the best site in this topic I have ever seen, the page of Marc Zimmer, here.

I think we had even too much of GFP now, so in the next posts we will go back to plasmids…